The present invention relates to a multi-speed gear system for a chain transmission device. More particularly, the invention relates to a simpler and lighter multi-speed gear system for a chain transmission device for a multi-speed bicycle.
Many bicycles include multi-speed transmissions to enhance their operation over different types of terrains. Existing bicycle transmissions are generally derailleur type manually controlled by a cable connected to a shift lever. Moving the shift lever changes the cable tension and moves the derailleur and a drive chain from one sprocket to another sprocket. Since the chain moves between sprocket wheels, the plane in which a driving sprocket that is connected to the pedals and the plane in which a driven sprocket that is connected to the rear wheel of the bicycle should be close if not identical. In addition, the diameters of adjacent sprockets cannot be much different because an abrupt reduction or increase of the diameter may cause the chain fail to be wound around the destination sprocket. Owing to these prior art multi-speed speed gear system for a bicycle includes many sprockets for both the driving sprocket and the driven sprocket sides. For example, for a speed change ratio from about 1:1 to 3:1, three driving sprockets and 9 driven sprockets are used, and there are 27 shift steps. Thus the speed change gained by one shift step is not appreciable. In order to get a comfortable feeling, the bicycle rider should repeat several steps of shifting. Also the plurality of sprockets increase the weight and cost of the bicycle.
The present invention contrives to solve the disadvantages of prior art.
Therefore, an object of the invention is to provide a simpler and lighter multi-speed gear system for a multi-speed bicycle.
Another object of the invention is to provide a multi-speed gear system that can provide a bigger speed change for a shift step.
Still another object of the invention is to provide a multi-speed gear system that can change speed in a single plane.
To achieve the above-described objects, the invention provides a multi-speed gear system for a chain transmission device of a bicycle that includes a disc having a front plate, a rear plate, and a plurality of tooth series concentrically arranged in the disc, and a tooth series selector. The front plate and the rear plate are spaced apart by a predetermined distance, and each of the tooth series has a plurality of tooth blocks. The front plate of the disc has a plurality of tooth holes, and the rear plate of the disc has a plurality of rear holes. Each of the tooth blocks is either pushed into a corresponding one of the tooth holes or protrudes out of the front plate, and in order to change speed, the tooth series selector selects one of the tooth series and makes the tooth blocks of the selected tooth series protrude out of the front plate. The front plate has apertures between the tooth holes and the rear plate has apertures between the rear holes to reduce the weight of the disc.
The tooth series selector makes the tooth blocks of the next radially outward tooth series protrude out of the front plate when the ratio of speed change becomes higher, and makes the tooth blocks of the next radially inward tooth series be pushed into the tooth holes when the ratio of speed change becomes lower.
The multi-speed gear system may further comprise a sprocket wheel and the diameter of the sprocket wheel is smaller than the diameter of the radially innermost tooth series.
Preferably, the number of the tooth series is five, and the ratio of speed change is in a range between about and about 1:1 and about 3.2:1. Also, preferably, the number of tooth blocks of each tooth series is about seven.
The tooth blocks of the tooth series are arranged so that the line connecting the center of one of the tooth blocks of one of the tooth series and the center of the corresponding tooth block of the adjacent tooth series is a curve. Preferably, the curve is spiral.
Each of the tooth blocks has a body, two teeth that protrude from the body, a projection that protrudes from the body, a guide portion that protrudes from the body between the teeth and the projection, a recess provided in the projection and the guide portion, a slot provided in the recess, a stop spring and a snap spring.
The stop spring and the snap spring are received in the recess. The stop spring protrudes out of the tooth block through the slot. When one of the teeth is pushed, the teeth are pushed into the tooth hole of the front plate of the disc, the snap spring snaps the tooth block in a position in which the teeth are pushed into the disc, the guide portion abuts the rear plate of the disc limiting further movement of the tooth block, and the projection protrudes out of the rear plate of the disc. When the projection is pushed into the rear hole of the rear plate of the disc, the snap spring snaps the tooth block in a position in which the projection is pushed into the disc, the stop spring abuts the front plate of the disc limiting further movement of the tooth block, the teeth protrude out of the front plate of the disc, and the guide portion contacts the tooth hole.
The tooth block further includes a hole in the recess to disassemble the tooth block from the disc.
The tooth series selector has a U-shaped selector body, an upper arm, a lower arm, and a pin connecting the upper arm and the lower arm. The selector body has a top wall, a bottom wall, and a side wall connecting the top wall and the bottom wall. The pin is pivotally attached to the side wall. The top wall has a plurality of pivoting blocks and the bottom wall has a polarity of pivoting blocks. The disc rotates between the top wall and the bottom wall. Each of the pivoting blocks is biased outside of the tooth series selector by a spring. The upper arm selectively push the pivoting blocks into the space between the top wall and the front plate of the disc and the selected pivoting block pushes the teeth of the tooth blocks of the selected tooth series into the tooth holes of the front plate. The lower arm selectively push the pivoting blocks into the space between the bottom wall and the rear plate of the disc and the selected pivoting block pushes the projections of the tooth blocks of the selected tooth series into the rear holes of the rear plate.
The upper arm and the lower arm are biased toward the original position by a return spring. A cable is attached to the lower arm, and the upper arm and the lower arm are rotated from the original position by pulling the cable. The upper arm has steps so that the upper arm pushes all of the pivoting blocks of the top wall at the original position and gradually releases more pivoting blocks starting from the radially innermost pivoting block as the upper arm is rotated further from the original position, and the lower arm has steps so that the lower arm releases all of the pivoting blocks of the bottom wall at the original position and gradually pushes more pivoting blocks starting from the radially innermost pivoting block as the lower arm is rotated further from the original position.
Each of the pivoting blocks includes two arc-shaped walls, two side walls making a predetermined angle, a flat wall and two curved walls connecting the flat wall and the two side walls. The two side walls, the two curved walls and the flat wall connect the two arc-shaped walls. The two side walls are symmetrically positioned and the two curved walls are symmetrically positioned. A first through hole is provided between one of the curved walls and one of the side walls, and wherein the tooth series selector further has a shaft that is received in the first through hole. Preferably, the predetermined angle is in the range between about 110 and about 120 degrees. Also, preferably, the two side walls are concave.
The pivoting block further includes a second through hole, and the tooth series selector further includes a rod received in the second through hole. The size of the second through hole is substantially larger than the size of the rod, and the rod limits outward rotation of the pivoting block when the pivoting block is released.
The pivoting block further includes a recess formed in the curved wall and the side wall, and the spring biasing the pivoting block outward is received in the recess and wound around the shaft of the tooth series selector.
The multi-speed gear system may further comprise a speed selector that is connected to the tooth series selector with the cable.
When the multi-speed gear system for a chain transmission device is used for a bicycle having a driving sprocket wheel driven by pedals of the bicycle, a driven sprocket wheel attached to a rear wheel of the bicycle, one or more tension sprocket wheels, and a chain wound around the sprocket wheels, the disc of the multi-speed gear system becomes the driving sprocket wheel.
The advantages of the present invention are numerous in that: (1) the multi-speed gear system includes only one sprocket wheel, thus is lighter and simpler; (2) the chain moves in a single plane for any shift step; and (3) shifting may be performed without driving the rear wheel of the bicycle.